Prevalence and Occlusion Characteristics

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Prevalence and Occlusion Characteristics
The frequency of CTOs depends on the type of patients studied with an incidence ranging between 10 and 30 % of all coronary angiograms.^1,2 More recent reports tend to show a lower incidence, possibly explained by the universal use of primary angioplasty and early revascularisation in acute coronary syndromes. Still, silent ischaemia or presence of atypical symptoms misinterpreted at the time of the acute event account for the consistent persistence of CTOs in 18.4 % of patients even in the most recent series.¹ You may expect that in patients with acute coronary syndromes CTOs are less frequent. In reality, even in patients with acute ST segment elevation myocardial infarction (STEMI), the incidence is 13 %.¹⁹ Interestingly, this subgroup of patients has a particularly poor immediate and long term prognosis. The presence of a CTO in a non-infarct-related artery was found to be a strong and independent predictor for both early mortality (within 30 days after STEMI) and late mortality (from 30 days to five years after STEMI).^19,20 Inability to provide collaterals to the occluded vessel and, vice versa, acute impairment of preexisting collaterals from the acutely occluded vessel to the CTO jeopardising a large myocardial territory are possible explanations of this phenomenon, which also explains the prognostic benefit of recanalising CTOs. Far greater prevalence of CTOs, exceeding 50 % of cases,¹ are identified in the subgroup of patients restudied after coronary artery bypass graft (CABG) implantation. Since interventions in degenerated bypass grafts have frequent embolic complications and poor long term durability, the recanalisation of the CTO in the native vessel is an appealing but often technically challenging alternative.²¹

Lesion characteristics play an important role in the likelihood of a successful recanalisation. Morino et al. introduced a lesion-related difficulty grading tool, the J-CTO score, based on a large series of anterograde recanalisations in Japan.²² Length greater than 20 mm, presence of a greater than 45 degrees bend within the occlusion, presence of intralesional calcification, delineation of a stump at the proximal end are four angiographic parameters shown to influence the percentage and time requested for anterograde recanalisation. With the addition of a fifth non-angiographic parameter derived from the clinical history, a previous failed attempt, it is possible to calculate the J-CTO score attributing to each of these parameters one point. ‘Easy’ lesions with a score of 0–1 had a success rate of greater than 90 % (97.8 % and 92.3 % respectively) and required a short time for wire crossing in most cases. Success progressively falls with an increased score with ‘difficult’ – J-CTO score equal or greater than 3 – lesions having a 73.3 % success rate and demanding a prolonged time for crossing.²² Technical progress and the introduction of the retrograde approach have certainly modified these percentages, probably cancelling the importance of some of these factors and shifting the field from lesion-related to collateral circulation-related predictive factors of failure. The presence and quality of the collaterals, their continuity and tortuosity, their location in the septum or in the epicardium, the angle of the collateral anastomosis with the CTO vessel become important factors if a retrograde strategy is considered.²³ Non-invasive imaging, in particular coronary multi-slice computed tomography (MSCT), can help delineate the characteristics of the CTO, by definition invisible because not opacified. With coronary MSCT the occluded segment can be better delineated, calcium more reliably detected and quantified, the tortuosity and vessel path followed, the true length of the lesion better defined.